james@bigtex.uucp (James Van Artsdalen) (05/22/88)
A bunch of people have called asking questions about my earlier comments that it is possible to use ESDI drives with unix/386. To clarify: The current unix/386 driver cannot support more than 17 sectors per track. The problem is that most (all?) ESDI drives have more than 17 sec/trk. For example, the CDC Wren III-182 has between 34 and 36 sec/trk depending on the configuration chosen. The Western Digital WD1007/WA2 controller gets around this type of problem by supporting emulation modes, wherein a 17 sec/trk geometry is emulated. For an ESDI drive, this is typically done by dividing the number of sectors by two to get exactly 17 sec/trk, and then doubling the apparent number of heads. Therefore, an eight head 34 sec/trk drive appears *at the register level* as a sixteen head 17 sec/trk drive. Since register level is all unix/386 cares about, it works. The only drawback here is that since sixteen heads is an absolute limit, you can't spoof drives with more than eight heads this way without losing some storage capacity. As an example, bigtex runs the CDC Wren III-182 ESDI drive. I use the WD1007/WA2 to make it appear that I have a 16 head, 17 sec/trk drive. I lose the ninth head for now, but the drive does work very well. Not only is it an extremely fast drive, but the 1007 is a buffering 1:1 interleave controller (also has floppy support on-board). An added bonus of the WD1007/WA2 is that you can "hide" defects on drives that can support more than 34 sec/trk. My Wren III is configured for 35 sec/trk, but only 34 are visible at the register level. The other sector on each track is placed over an defect present, so that there are always 34 defect-free sectors available on each track. A minor note is that this is exactly what the Compaq 386/20 does with its 130meg drive: it's a brain-damaged CDC Wren III-182 (that's why there's only 130meg instead of the factory-spec. 150meg) and an older variant of the WD1007 (no floppy support I think - rumor only here). uPort's BBS is using ESDI drives last I heard. Bottom line: you can use ESDI drives today, but only with the WD1007 or similar controller that emulates a 17 sec/trk drive at the register level. Works fine. Only drawback is that you may lose some space, but once uPort releases their updated hd driver, you can get it back by turning off emulation. -- James R. Van Artsdalen ...!ut-sally!utastro!bigtex!james "Live Free or Die" Home: 512-346-2444 Work: 328-0282; 110 Wild Basin Rd. Ste #230, Austin TX 78746